Process and devices are known to separate a conglomerate of substances into the various individual substances by cutting the conglomerate using a shredder in order to prepare the substances for re-usage. Conglomerates of materials made from plastic materials of different chemical composition and density are to be separated in a flotation process, whereby the heavier plastic material settles on a screen bottom in a flotation tank and will from there be removed. Flotation liquid normally is pure water. In order to achieve a clear separation of plastic materials of different density in pure water, undesired movements of the flotation liquid should unalterably be avoided or at least such movements should be restricted to a minimum.
Together with a conglomerate of plastic materials, prepared by a shredder, ferromagnetic and non-magnetic metal stuff or other materials, heavier than plastic materials, will enter into the flotation tank and will settle on the screen bottom, preferably in small heaps. Lighter plastic materials in such conglomerate need more time for settling than heavier particles, and hence, together with flotation liquid, will be removed from the upper part of the flotation tank. A separation of plastic materials in accordance with their density did at that stage not yet take place. That separation of plastic materials in accordance with their density happens in a second follow-up stage. Materials, heavier than plastics, which settled in the course of the first stage on the screen bottom lead to serious problems, since they close the openings of the screen bottom and prevent a free flow of flotation liquid. Efficiency of the separation process of a conglomerate of stuff is therefore seriously affected.
One object of this invention is to develop a process for separation of plastic material from other stuff of a various density by a flotation process in a liquid bath. Conglomerates of plastics fed into flotation baths often contain metals—iron and non-ferrous components and other stuff—that are heavier than plastics. This stuff in the conglomerate to be separated is heavier than plastics and therefore quickly settles on the screen bottom while particles of plastics are still floating in the flotation bath. Still floating particles of plastics are transferred to a second stage of flotation and separated in accordance of their differing density. Heavier stuff of the conglomerate that settle in the first stage easily lead to a closure of the openings for liquid passing through screen bottom. It is, therefore, one object of this invention to discharge this stuff, that mostly settles as heaps on the screen bottom, avoiding disliked motion of flotation liquid in flotation tank, in order to prevent that stuff already settled again floats and mixes with still floating plastic particles. This invention recommends that a movable screen bottom slowly moves in the direction of reducing a slot that exists between one edge of screen bottom and the wall of the flotation tank and then after having reached a final position to quickly and abruptly move in the counter-direction. That movement occurs in intervals. This abrupt motion of the screen bottom initiates that kinetic energy accumulated in the heaps of metal and other heavy stuff moves this stuff towards the slot-edge and through the slot into a collection-container underneath the screen bottom. From there this stuff can be discharged without any problem.
Hence, one object of this invention is to eliminate these heaps of metals on the screen bottom during operation without having any adverse influence on the separation process for plastic materials from metals or other heavy staff. Scraping or washing off of such particles is to be avoided, since that would create undesired motion in the flotation tank and hence, would have a negative influence on the separation process for plastics of different density from other stuff.